Non-Invasive Estimation of the Upper Boundary of the Severe Intensity Exercise Domain: The Maximal Accumulated Oxygen...

The aim of this study was to evaluate whether the highest power output at which the predominant energy contribution is derived from the aerobic system (aerobic limit power: ALP), as estimated using maximal accumulated O₂ deficit (MAOD) method, corresponds to the upper boundary of the severe intensity exercise domain. Thirteen males completed: (i) a ramp incremental exercise test, (ii) four submaximal constant power exercise tests, and (iii) 6-7 maximal and at least one supramaximal constant power exercise tests. The upper boundary of the severe intensity exercise domain was estimated based on the linear relationship between the time to achieve $\dot{V}$ O_2max and the time to task failure (P_UPPERBOUND). The ALP was estimated by MAOD method, i.e. based on the difference between the predicted $\dot{V}$ O₂ demand derived from a linear regression line from submaximal exercise tests and the accumulated O₂ uptake calculated by integrated $\dot{V}$ O₂ data. The highest power output at which the aerobic energy contribution rate was still predominant (i.e., 50%+) was defined as the ALP. Based on the principal results, ALP estimated by MAOD was not significantly different from the P_UPPERBOUND (390 ± 58 vs. 387 ± 61; p = 0.16; effect size: 0.42) and they were closely aligned (r: 0.99; bias: 3 ± 7 W; standard error of estimation: 7 W; limits of agreement: -11-17 W). Consequently, ALP, as derived from the MAOD method, provides a non-invasive alternative to accurately determine the P_UPPERBOUND with less physiological stress.